This invention relates to a color conversion filter, a color filter, and a method of manufacture thereof. In particular, this invention relates to a color conversion filter, color filter, and method of manufacture thereof, used in forming a display by lamination with a light-emitting member.
A color conversion method is a method for realizing multicolor light emission using organic EL elements. In the color conversion method, a color conversion layer, which absorbs light emitted by an organic EL element and emits light with a wavelength distribution different from the absorbed wavelengths, is placed in front of the organic EL element, to express multiple colors. In Patent Reference 1 (identified below) and elsewhere, a resin dispersed-type color conversion layer is disclosed, in which a fluorescent dye is dispersed in a polymer resin, as such a color conversion layer. In color conversion methods, single-color emitting organic EL elements can be used, so that manufacturing is facilitated. Hence energetic studies are underway on application of organic EL elements having color conversion layers to large-screen displays.
Further, such display types have the characteristic that satisfactory color reproducibility is obtained by combining a color conversion layer and a color filter. However, in order to obtain adequate efficiency from such a resin dispersed-type color conversion layer, the film thickness must be made as thick as approximately 10 μm. Further, special technologies are required, such as technology for flattening roughness in the color conversion layer in order to form the organic EL element on the upper face thereof, and technology to shut out moisture appearing from the color conversion layer, and these contribute to drive up the cost of display panels.
As a measure to resolve the above problems, methods for forming layers having color conversion functions using dry processes, such as evaporation deposition and sputtering methods, have been proposed. In such methods, color conversion layers with a film thickness of 2 μm or less can be formed, but there is the problem that highly precise patterning (for example, at 150 ppi or higher) is difficult.
As a method which further develops the above-described measure, a method is conceivable in which an ink comprising the constituent material is prepared, and an inkjet method is used to form a patterned color conversion layer. Advantages of the inkjet method are the high efficiency of use of ink, and the ability to hold down the cost of manufacture of the color conversion layer.
However, it is known that when performing precise patterning, there is a need to suppress shifts in the position of impact of dispensed ink drops, and to suppress protrusion into adjacent pixels after impact. As means for resolving such problems, methods have been proposed in which banks are formed on the substrate side (see Patent Reference 2 and Patent Reference 3, which are identified below). In order to more effectively fabricate high-precision patterns using banks, a method is also proposed in which surface treatment using plasma treatment or similar according to the bank material is performed, and banks having a layered structure of different materials are formed (see Patent Reference 3).
When a color conversion filter is used in an organic EL display having a top-emission structure, in general a configuration is employed in which an organic EL substrate having a plurality of light-emitting portions and a color conversion filter are laminated. At this time, if the gap between the substrate and the color conversion filter is too great, there is the problem that light emitted by the light-emitting portions intrudes into adjacent pixels or subpixels (crosstalk). On the other hand, if the gap is too narrow, there are concerns regarding the effects of interference and/or mechanical contact with the light-emitting region. In particular, in an organic EL display using the color conversion method, the light quantity incident on the color conversion layer greatly contributes to the conversion efficiency, and so control of the gap using spacers is important.    Patent Reference 1: Japanese Patent Laid-open No. H8-286033.    Patent Reference 2: Japanese Patent Laid-open No. 2005-203215.    Patent Reference 3: Japanese Patent Laid-open No. 2000-353594.    Patent Reference 4: Japanese Patent Laid-open No. 2003-243154.
As is disclosed in Patent Reference 4, it is known that in an organic EL display with a top-emission structure, by filling the gap with epoxy resin or another resin and increasing the refractive index in the gap, the efficiency of light extraction is improved. However, in general epoxy resins and other resins have high viscosity, and so are difficult to spread uniformly in the gap during lamination. Particularly in the case of a color conversion filter in which banks are formed, when using a simple dripping lamination method, the resin does not spread everywhere on the inside of the outer periphery seal material, so that even in a panel measuring approximately two to three inches, a portion of the screen is not filled with resin, and the problem of uneven brightness occurs.
In the color conversion filter 2000 of the prior art shown in FIG. 2, a spacer portion 280 is fabricated on the bank layer 260, so that depending on the conditions of the photolithography method used, acute-angle portions may occur in the shape of the joined portion of the spacer 280 and the bank 260. Consequently, in the prior art color conversion filter 2000, the barrier layer 270 is not adequately covered on the spacer portions 280 and bank layer 260, so that gaps tend to occur near portions at which there are acute angles in the joining portion of the barrier layer 270. As a result, when the color conversion layer 220 is vulnerable to water and/or oxygen, moisture from these gaps may reach the color conversion layer 220 either via the interface with the barrier layer 270, the spacer portions 280 and bank layer 260, or through moisture absorption by the spacer portions 280 and bank layer 260 themselves, so that the lifetime of the color conversion layer 220 is significantly harmed.
Hence in order to manufacture a high-precision, high-efficiency organic EL element, (1) prevention of ink leakage into regions other than the subpixel (in particular, into adjacent subpixels) to form the desired color conversion layer in the prescribed subpixels, and (2) precise control of the gap with the substrate in lamination of the color conversion filter to the organic EL substrate, and uniform filling of the gap with resin, are sought.
Further, in the color conversion filter 2000 of the prior art shown in FIG. 2, the bank layer 260 exists discontinuously on the substrate relative to the display portion, in a ratio of from 10 to 20%. The spacer portions 280 are formed on the bank layer. As the fineness of the pixels increases, for a width of the bank layer 260 of 10 to 15 μm, the width of the spacer portions 280 also becomes approximately 10 μm, a magnitude extremely close to that of the bank layer 260. In such a case, the spacer portions 280 formed on the bank layer 260 tend to protrude due to shifts in the photomask position, and unevenness occurs in the heights of the spacer portions 280. Hence when forming spacer portions 280 of the prior art, the photomask must be aligned with high precision.
Further, when after formation of the bank layer 260 the material layer of the spacer portions 280 is applied onto the bank layer 260, in order to form the layer with the desired film thickness without unevenness, it is extremely difficult to control the viscosity and/or solid fraction of the resin applied and formed, and to control the rotation rate and similar.